Outline

Objective: Because of limited availability of autologeous bone graft and donor site morbidity bone substitutes become more and more important in spinal surgery as well as in filling of larger burr hole defects of the skull. As a new hydroxylapatite-based bone substitute (NanoboneÂ®) has already been established for use in craniomaxillofacial surgery with promising results we initiated a prospective study to prove its sufficient bone graft potential for interbody fusion. A special characteristic of nanostructured materials in comparison to bulk material is the existence of an extreme high number of molecules on the surface. This new material is characterized by nanocrystalline hydroxyapatite embedded in a matrix of silica gel, which is porous down to the nanometer size range (porosity of the material is 61%; internal surface is 84 m2/g).

Methods: Fifteen patients (7 women, 8 men; ageing from 47 to 69 years) with a total number of 32 intervertebral spaces to fuse were included in the present study. Indications were: spondylolisthesis, spinal stenosis with degenerative instability, scoliosis, and postdiscectomy syndrome. All patients underwent instrumented single- or multi-level PLIF-procedures. After nine months follow-up a CT-scan was performed to demonstrate the grade of bony bridging between the endplates of the fused vertebrae. Furthermore we report about a patient who underwent two consecutive biopsies of the frontal lobe for tumour. Because of aesthetic reasons the burr hole approach has been filled up with the bone substitute. The harvested material from the second biopsy 48 days later could be histologically analyzed.

Results: All patients have passed the 9 month CT scan with 3D-reconstruction. Twenty seven out of 30 (two segments had to be excluded because of instrumentation failure and primary cage displacement) corresponding segments showed a solid interbody fusion (90%). Graft related side effects were not observed. The clinical scores (ODI and VAS) showed a significant reduction compared to the preoperative values. The histological examination of the burr hole material showed high amount of early bone formation as compared to former animal studies.

Conclusions: A new nanostructured HA-based bone substitute has been evaluated for the use in neurosurgery. Compared to the literature revealing a fusion rate of 70 to 100%, the present fusion rate of 90% in our study and our experiences in bone defect filling indicate a safe application as well as a high osteogenetic ability of this new bone substitute with a potential to be widespread used in neurosurgery.